The vibratory mill is of the type in which the mill contains grinding bodies. These grind down the material that is to be treated and expose the treated material to powerful blows, which lead to the surface energy and chemical reactivity of the ground particles increasing.
The Swedish patent number 524 393 “Method for treatment of fly ash” and the Swedish patent number 524 154 “Process for producing blended cements with reduced carbon dioxide emissions” describe such grinding processes.
Here, the mechanical activation of Portland cement is described, together with that of various other materials such as fly ash, granulated blast furnace slag (GBFS), and finely divided quartz sand mixed at various proportions, by the use of a vibratory mill with grinding bodies and with an amplitude of vibration of 2-20 mm and a frequency of 800-2,000 vibrations per minute.
A second vibratory mill is a mill denoted VBM 3034, manufactured by Metso Minerals, Finland.
A major disadvantage of existing vibratory mills is that the ratio of length to diameter is small, and this leads to a short retention time for material that circulates in the mill.
The Canadian patent CA 569381 describes a vibratory mill of the present type.
The mill has a grinding chamber with a wall at each end of the chamber. An inlet for material that is to be treated is located at the upper part of the chamber. An outlet is located at the opposite end of the chamber at the lower part of the chamber. A wall is present inside the chamber, at the end at which the outlet is located, provided with openings that allow the passage of material that has been sufficiently ground, which material falls down towards the outlet after it has passed the wall that is provided with openings. An impenetrable wall is present at approximately the centre of the chamber and located in its upper part, which wall prevents material being transported directly from the input through the upper part of the mill to the wall that is provided with openings and through this to the outlet, which, in combination with the above-mentioned ratio of length to diameter, would lead to a very short retention time in the mill. This impenetrable wall, however, is subject to extensive wear by the grinding bodies, and it must for this reason be exchanged approximately every third day. This leads, naturally, to interruption in service and thus costs.
The present invention solves this problem.